1. Technical Field
The present invention relates to methods for repairing spinal disorders. More particularly, the present invention relates to a method of repairing spinal disorders, especially those requiring spinal fusion, using a biocompatible osteogenic band which induces new bone growth formation at the site of implantation.
2. Description of the Related Art
The vertebral column (spine) is a biomechanical structure composed of a series of joints known as motion segment units. Each motion segment unit includes two adjacent vertebrae and their facet capsules, the intervertebral disc, and connecting ligament tissue. The spine is divided into four major regions which include the cervical, thoracic, lumbar and sacral regions and functions to protect the spinal cord and nerve roots, and provide support to the body. The intervertebral disc is located between the two endplates of adjacent vertebrae and is composed of the nucleus pulposus (a gel-like ball located at the center of the disc) and annulus fibrous (collagen fibers surrounding the nucleus pulposus). The intervertebral disc stabilizes the spine, and provides the spine with resiliency and the ability to withstand compression, rotation and bending strain. The facet capsules are bony elements which aid in the support of compressive loads and resist torsional motion. Ligaments connected to the spine support loads in tension and help provide spinal stability by limiting excessive range of motion and absorbing energy applied due to trauma.
Various types of spinal disorders are known and include kyphosis (backward curvature of the spine), spondylolysis, spondylolisthesis (forward displacement of a lumbar vertebrae), scoliosis (abnormal curvature of the spine) and disorders involving ruptured, slipped, damaged and diseased discs, damaged vertebrae, and the like. Patients suffering from the aforementioned disorders typically experience severe pain, numbness, decreased mobility, muscle weakness and nerve damage.
Spinal fusion is frequently used as a treatment for such disorders and is achieved by formation of a bony bridge between adjacent motion segments eliminating the intervertebral joint. Spinal fusion can be accomplished within the disc space, anteriorly between adjacent vertebral bodies and/or posteriorly between consecutive processes, e.g., transverse processes, laminae or other posterior elements of the vertebrae.
One frequently used spinal fusion technique involves removal of the intervertebral disc and insertion of an anterior supporting structure, e.g., bone grafts, bone substitutes, plugs, bone dowels, cages, and the like, into the intervertebral disc space to prevent collapse of the disc space and promote fusion of the adjacent vertebrae. To ensure proper growth and fusion between the affected adjacent vertebrae, the posterior side of the spine is frequently stabilized by utilizing a rigid metallic implant, e.g., a plate, rod, wire or strip, which spans the adjacent vertebrae to re-create a load distribution similar to that of the intact spine. These metallic implants are commonly referred to throughout the relevant scientific and medical literature as xe2x80x9ctension bands.xe2x80x9d
The use of such metallic implants to stabilize the spine and facilitate fusion presents several disadvantages. One disadvantage encountered utilizing such metallic implants is that once fusion occurs the metallic implant becomes superfluous and remains as a permanent foreign fixture. As the metallic implant loosens enough to allow relative motion, particulates are generated as wear debris. This wear debris then has the potential to cause a foreign body response. Metallic implants are also subject to fatigue failure due to repeated cyclic loading. An implant that is remodeled, and then repaired as it later becomes damaged, will not fail due to fatigue. Another disadvantage is that the implanted metallic implant itself possesses ferromagnetic properties and thus prevents the use of post-operative plain film X-rays, MRI or CT scan imaging due to scattering of the image. Yet another disadvantage is that when such metallic implants are placed over bone tissue, any tension load placed on the spine is transmitted to the implant rather than the bone tissue, thereby xe2x80x9cstress shieldingxe2x80x9d the bone. Over a period of time, bone tissue that is shielded from tension loads is removed by the body thereby weakening the structure of the bone. Accordingly, removal of the implant by a second operation may be required to prevent loss of bone tissue caused by stress shielding.
In view of the aforementioned limitations posed by using rigid metallic implants to stabilize the spine and facilitate fusion, there is a need to provide a method of treating spinal disorders that will provide for the fusion of bone at the implant site, thereby providing a graft that will not fail mechanically or cause rejection in the patient, and will not require removal in a subsequent operation.
Therefore, it is an object of the present invention to provide a method of stabilizing the spine which overcomes the limitations of rigid metallic implants.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that is non-antigenic and will not be rejected by the host.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that is biocompatible and will not require removal in a subsequent operation.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that is osteogenic and that adequately supports tension loads.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that will avoid stress shielding.
It is a further object of the present invention to provide a method of stabilizing the spine with a device that supports fusion between adjacent vertebrae.
It is a further object of the present invention to provide a method of stabilizing the spine with a device which can be utilized in conjunction with an anterior supporting structure.
Other objects of the invention will be apparent to those skilled in the art in view of the above objects and the foregoing specification.
These and further objects of the invention are obtained by a method for repairing a spinal disorder which comprises affixing a biocompatible osteogenic band to two or more vertebrae of a spine to maintain the two or more vertebrae under tension, wherein the band is fabricated in whole or in part from biocompatible fibers of a native, biosynthetic, or synthetic polymeric, connective tissue or plant connective tissue-like containing component that is osteoinductive or has been treated to be osteoinductive. The osteogenic material can include bone, tendon, ligament, silk, collagen, elastin, reticulin, cellulose, alginic acid, chitosan, small intestine submucosa, biocompatible polymers or combination thereof which has been rendered osteogenic by one or more procedures described hereinbelow. A suitable material is disclosed in the U.S. Provisional Application filed on even date herewith under Certificate of Express Mail # EL713572920US, the contents of which are incorporated by reference herein.
A method for repairing a spinal disorder is also provided which comprises inserting an anterior supporting structure into a disc space between adjacent vertebrae of a spine and affixing a biocompatible osteogenic band to two or more vertebrae of the spine to maintain the two or more vertebrae under tension.
Affixation of the foregoing biocompatible osteogenic band to the spine leads to new bone ingrowth by one or more biological mechanisms such as osteogenesis, osteoconduction and/or osteoinduction or by one or more physical mechanisms such as providing a support for new bone growth. The expression xe2x80x9costeogenic materialxe2x80x9d as utilized herein shall therefore be understood as referring to a material which will participate in the process of new bone growth regardless of the mechanism(s) involved. The osteogenic material can be obtained from sources which are not in themselves osteogenic but are rendered osteogenic by incorporation and/or associating therewith one or more osteogenic components. Accordingly, unlike metallic implants, the biocompatible osteogenic band of this invention contributes to the development of a fusion preferably across vertebral bodies of the posterior spine and aids in the repair and stabilization of the spine.
Another advantage of the present invention is that the biocompatible osteogenic band preferably provides posterior tensile loading, thereby recreating a load distribution similar to that of the intact spine.
Another advantage of the present invention is that, unlike conventional metallic implants, the biocompatible osteogenic band is sufficiently flexible to allow affixation to a vertebral site yet sufficiently strong, tough and inextensile to withstand applied excessive force. Because the material is osteogenic, new bone is formed around and within the implant and the biocompatible osteogenic band is incorporated with new bone tissue via the process of remodeling. Accordingly, unlike a metallic implant which persists long after its useful life, it is not necessary to remove the biocompatible osteogenic band in a subsequent operation.
Another advantage of the present invention is that, unlike conventional metallic implants, the biocompatible osteogenic band will not stress shield the bone. In addition, unlike metallic implants, the biocompatible osteogenic band does not interfere with the use of post-operative plain film X-rays, or MRI and CT scans.
Other advantages of the present invention will become apparent to one skilled in the art from the following written description and accompanying figures.